c. 1300, ranclen, of a sore, wound, etc., "to fester," from Old French rancler, earlier raoncler, draoncler "to suppurate, run," from draoncle "abscess, festering sore," from Medieval Latin dracunculus, literally "little dragon," diminutive of Latin draco "serpent, dragon" (see dragon). According to OED (citing Skeat and also Godefroy's "Dictionnaire De L'ancienne Langue Française"), the notion is of an ulcer caused by a snake's bite. Transitive meaning "cause to fester" is from c. 1400. Figurative use, of feelings, etc., is from 16c. Related: Rankled; rankling.
Middle English roten, from Old English rotian, of animal substances, "to decay, putrefy, undergo natural decomposition" (intransitive), also of vegetable matter," from Proto-Germanic *rutjan (source also of Old Saxon roton, Old Norse rotna, Old Frisian rotia, Middle Dutch roten, Dutch rotten, Old High German rozzen "to rot," German rößen "to steep flax"), from stem *rut-. Related: Rotted; rotting.
By c. 1200 as "fester or decay morally, become morally corrupt." Transitive sense of "cause decomposition in" is from late 14c. To rot in prison (mid-14c.) suggests wasting disease.
late 14c., bocchen "to repair," later, "repair clumsily, to spoil by unskillful work" (1520s); of unknown origin. Middle English Compendium says probably the same as bocchen "to swell up or fester; to bulge or project" (though this is only from early 15c. and OED denies a connection) which is from Old North French boche, Old French boce, a common Romanic word of uncertain origin. Related: Botched; botching.
As a noun, "a bungled or ill-finished part," from c. 1600, perhaps from the verb, but compare Middle English bocche "a boil, a pathological swelling, a tumor" (late 14c.), used especially of glandular swellings from the plague, also figuratively "a corrupt person; a rotten condition" (late 14c.), "a hump on a cripple" (early 14c.), which probably is from Old North French boche, Old French boce, a common Romanic word of uncertain origin.